SOX tolerant NOX trap catalysts and methods of making and using the same

ABSTRACT

The present invention relates to sulfur tolerant catalyst composites useful for reducing contaminants in exhaust gas streams, especially gaseous streams containing sulfur oxide contaminants. More specifically, the present invention is concerned with improved NOx trap catalysts for use in diesel engines as well as lean burn gasoline engines. The sulfur tolerant NOx trap catalyst composites comprise a platinum component, a support, and a NOx sorbent component prepared by hydrothermal synthesis. The NOx sorbent component comprises a first metal oxide and a second metal oxide. The metal in the first metal oxide is selected from the group consisting of aluminum, titanium, zirconium, silicon, and composites thereof, and the metal in the second metal oxide is selected from the group consisting of Group IIA metals, Group II metals, Group IV metals, rare earth metals, and transition metals. The metal in the first metal oxide is different from the metal in the second metal oxide. The sulfur tolerant NOx trap catalyst composites are highly effective with a sulfur containing fuel by trapping sulfur oxide contaminants which tend to poison conventional NOx trap catalysts. The sulfur tolerant NOx trap catalyst composites are particularly suitable for diesel engines because the composites can be regenerated at moderate temperatures with rich pulses, rather than at high temperatures.

BACKGROUND OF THE INVENTION

[0001] This application is a continuation-in-part of U.S. Pat.application Ser. No. 09/771,280, filed Jan. 26, 2001.

[0002] 1. Field of the Invention

[0003] The present invention relates to sulfur tolerant catalystcomposites useful for reducing contaminants in exhaust gas streams,especially gaseous streams containing sulfur oxide contaminants. Morespecifically, the present invention is concerned with improved NOx trapcatalysts for use in diesel engines as well as lean burn gasolineengines. The sulfur tolerant NOx trap catalyst composites comprise aplatinum component, a support, and a NOx sorbent component prepared byhydrothermal synthesis. The NOx sorbent component comprises a firstmetal oxide and a second metal oxide. The metal in the first metal oxideis selected from the group consisting of aluminum, titanium, zirconium,silicon, and composites thereof, and the metal in the second metal oxideis selected from the group consisting of Group IIA metals, Group IIImetals, Group IV metals, rare earth metals, and transition metals. Themetal in the first metal oxide is different from the metal in the secondmetal oxide. The sulfur tolerant NOx trap catalyst composites are highlyeffective with a sulfur containing fuel by trapping sulfur oxidecontaminants which tend to poison conventional NOx trap catalysts. Thesulfur tolerant NOx trap catalyst composites are particularly suitablefor diesel engines because the composites can be regenerated at moderatetemperatures with rich pulses, rather than at high temperatures.

[0004] 2. Related Art

[0005] Diesel powered vehicles represent a significant portion of thevehicle market worldwide. In Europe, the market share of dieselpassenger cars is about one third and is expected to grow even higher inthe years ahead. Compared to gasoline powered vehicles, diesel vehiclesoffer better fuel economy and engine durability. As diesel passengercars become more popular both in Europe and elsewhere, emissionsreduction is an increasingly urgent issue. In fact, Euro Stage IVregulations (year 2005) are calling for a 50% reduction of NOx emissions(0.25 g/km) compared to the Stage III (year 2000) level (0.5 g/km). Forsome vehicles, it would be difficult to meet the Euro IV NOx emissionstarget by engine improvement alone. It may be impossible to meet Euro VNOx regulations (0.125 g/km) without highly efficient after-treatmenttechnologies.

[0006] Reducing NOx from diesel exhaust is very challenging. The 3-waycatalyst technology, which is widely used in the gasoline cars, is notoperational in diesel vehicles. A 3-way catalyst requires the exhaustemissions near a stoichiometric point, neither fuel rich (reducing) norlean (oxidizing), while diesel emissions are always lean. In the early90's, the concept of NOx trap catalyst was explored for gasoline partiallean burn (PLB) engines where the NOx catalyst would trap NOx in a leanenvironment and reduce it in a rich environment.

[0007] To apply the NOx trap concept to diesel passenger cars, somespecial issues related to diesel emission characteristics needed to beaddressed. The exhaust temperature for light-duty diesel vehicles istypically in the range of 100 400° C., which is much lower than thegasoline exhaust. Therefore, low temperature oxidation activity andreduction during a rich spike is critical. One of the most difficultchallenges in applying this concept is the issue of sulfur poisoning.The exhaust sulfur forms a very strong sulfate on any basic metal site,which prevents the formation of nitrate, rendering the catalystineffective for trapping NOx. As with other catalytic converters,thermal stability is another important issue for practical application.

[0008] The operation of a NOx trap catalyst is a collection of a seriesof elementary steps, and these steps are depicted below in Equations1-5. In general, a NOx trap catalyst should exhibit both oxidation andreduction functions. In an oxidizing environment, NO is oxidized to NO₂(Equation 1), which is an important step for NOx storage. At lowtemperatures, this reaction is typically catalyzed by precious metals,e.g., Pt. The oxidation process does not stop here. Further oxidation ofNO₂ to nitrate, with incorporation of an atomic oxygen, is also acatalyzed reaction (Equation 2). There is little nitrate formation inabsence of precious metal even when NO₂ is used as the NOx source. Theprecious metal has the dual functions of oxidation and reduction. Forits reduction role, Pt first catalyzes the release of NOx uponintroduction of a reductant, e.g., CO (carbon monoxide) or HC(hydrocarbon) (Equation 3). This may recover some NOx storage sites butdoes not contribute to any reduction of NOx species. The released NOx isthen further reduced to gaseous N₂ in a rich environment (Equations 4and 5). NOx release can be induced by fuel injection even in a netoxidizing environment. However, the efficient reduction of released NOxby CO requires rich conditions. A temperature surge can also trigger NOxrelease because metal nitrate is less stable at higher temperatures. NOxtrap catalysis is a cyclic operation. Metal compounds are believed toundergo a carbonate/nitrate conversion, as a dominant path, duringlean/rich operations. The sulfur poisoning of a NOx trap catalyst isdepicted below in Equations 6-7. In Equation 6, S occupies a site forNOx and in Equation 7, SOx replaces CO₃ or NOx.

[0009] Oxidation of NO to NO₂

NO+1/2O₂→NO₂  (1)

[0010] NOx Storage as Nitrate

2NO₂+MCO₃+1/2O₂→M(NO₃)₂+CO₂  (2)

[0011] NOx Release

M(NO₃)₂+2CO→MCO₃+NO₂+NO+CO₂  (3)

[0012] NOx Reduction to N₂

NO₂+CO→NO+CO₂  (4)

2NO+2CO→N₂+2CO₂  (5)

[0013] SOx Poisoning Process

SO₂+1/2O₂→SO₃  (6)

SO₃+MCO₃→MSO₄+CO₂  (7)

[0014] In Equations 2, 3, and 7, M represents a divalent metal cation. Mcan also be a monovalent or trivalent metal compound in which case theequations need to be rebalanced.

[0015] Comparative investigations on the currently most discussed leanburn DeNOx technologies comprising the continuously operatingselectively catalytic reduction (SCR) of V-, Pt-, Ir-technologies aswell as the discontinuously operating NOx adsorption technology suggestthat the latter technology shows the most promising overall performancein terms of NOx, HC and CO removal in view of the proposed EURO III/IVlegislation. The sulfur concentration yields decisive influence on thelong-term activity of the NOx adsorption catalysts and it is shown by aworst case study, that even the use of low-sulfur fuel does not preventthe accumulation of sulfur on the NOx adsorption catalyst. Theaccumulation of sulfur on the catalyst has to be counteracted by anengine induced desulfation strategy, by which the sulfur is driven outof the NOx adsorption catalyst. This requires the provision of reducingexhaust gas at elevated temperature for a short period of time. Anoptimization of the desulfation parameters is mandatory in order tosuppress the formation of H₂S. It is conjectured that the thermaldegradation of the NOx adsorption catalyst proceeds via two differentdeactivation modes. The first one is based upon the loss of Ptdispersion and is accelerated by the presence of oxygen while the secondone can be traced back to the reaction between NOx storage componentsand the porous support material. Wolfgang Strehlau et al., Conference“Engine and Environment” 97.

[0016] Direct injection technology for diesel engines as well as forgasoline engines are the most favored ways to reduce the CO₂ emissionsin the future. NOx adsorber technology for gasoline DI engines as wellas for HSDI diesel engines is the favored technology to meet futureemission limits. Adsorber catalysts have demonstrated their potential tomeet future emission legislation levels on prototype basis for gasolineand diesel engines. Improving the NOx adsorber technology and theintegration of the adsorber system into the powertrain for theintroduction into the European market is the challenge for the nearfuture.

[0017] Using a catalyst cannot reduce much NOx pollutant in a lean burncondition. Abating NOx by a catalyst is very difficult in a lean(oxidation) environment. So far, use of any known catalysts (without aNOx trap) has achieved only very low conversion %. In order to convertNOx to N2, a reducing atmosphere is required. In the normal workingcondition of a diesel or lean burn engine, there is no reducingatmosphere, but always a lean (oxidation) engine out gas flow. Undersuch lean condition, NOx goes through the exhaust, as a pollutant, withlittle or no reduction.

[0018] A NOx trap traps (adsorbs) NOx in a lean environment so that NOxis depleted from the exhaust gas stream. However, once the limitedcapacity of the trap is used up, no more NOx will be trapped. A NOx trapis useful only when it can be regenerated. For instance, barium oxidecan be used as a regenerable NOx trap. In lean (oxidation) environment,barium oxide continues to trap NOx and form nitrate until its capacitybeing used up. To regenerate the trap, the gas flow is switched to rich(reducing) for a short period of time, when NOx is desorbed quickly fromthe trap, forming N₂, and the trap is regenerated back to barium oxide.Engine management or a hydrocarbon injection can be used to create thisrich environment. After regeneration, the NOx trap (ideally) recoversits full capacity as a fresh trap. Thus, an ideal NOx trap continuouslyworks in the alternative lean/rich environment.

[0019] During the regeneration (rich) period, NOx is released but notout the exhaust as a polluntant. Because a catalyst is used inconjunction with the trap, the released NOx is reduced to NOx is reducedto N₂ in the reducing (rich) environment. Therefore, in the regenerationperiod, not only the NOx trap is genenerated, but also the released NOxis converted to harmless N₂ and CO₂.

[0020] If no SOx apperas in the gas stream, many NOx traps includingbarium oxide, work well. Unfortunately, there is always SOx. Althoughthe amount of Sox is much less than NOx (e.g. SOx:NOx=1:100) SOx willeventually poison the NOx trap. This because that SOx is much strongerreactant than NOx. Once SOx is absorded on site of the trap, it sticks(forms sulfate). SOx competes for sites with NOx and the trap iseventually poisoned. In addition, sulfated barium NOx trap cannot beregenerated (sulfated barium oxide needs a much higher temperature toregenerate than that of a normal NOx regeneration process).

[0021] The underlying theory of hydrothermal synthesis and the apparatusused is described in “Hydrothermal Synthesis”, George W. Morey, Journalof the American Ceramic Society, Sep. 1, 1953. By way of illustration,the determination of the compositions of coexisting gas and liquidphases in the system H₂O—Na₂O—SiO₂ at 400° C. are discussed.

[0022] The hydrothermal synthesis of lead titanatc is reported toinvolve the treatment of lead and titanium containing aqeous feedstockat temperatures ranging from 200° C. to 300° C. at autogenous pressures.Suitable sources of lead and titanium can be the oxides, or metalhydrous oxides derived from perchlorates, nitrates, acetates oralkoxides. Titanium isopropoxide and lead acetate have been used tostudy the hydrothermal synthesis of lead titanate particles. Twomechanisms are involved in the synthesis of lead titanate particles: 1)dissolution of the hydrous metal oxide feedstock followed byprecipitation and, 2) in situ crystallization of the hydrous oxideparticles. “Hydrothermal Formation Diagram In The Lead Titanate System”D. J. Waston et al., Ceram. Trans, 1988, vol 1, Ceram Powder Sci. 2, Pt.A,154-162.

[0023] The advantages of the hydrothermal synthesis of Ba-polytitanatesin the form of fine has been reported in connection with microwaveapplications. “Hydrothermal precipitation and characterization ofpolytitanates in the system BaO-TiO₂” T. R. N. Kutty et al., Journal OfMaterials Science Letters 7, 601-603(1988).

[0024] U.S. Pat. No. 3,963,630 (Yonezawa et al.) discloses a process forproducing crystalline powder of a composition represented by theformula, PbTi_(q)Zr_(p)O₃. In the formula, q and p represent moleratios, the sum of q and p is equal to 1.00, the mole ratios q is notsmaller than 0.45 and not greater than 0.90, the mole ration p is notsmaller than 0.10 and not greater than 0.55. The process comprises thesteps of preparing an acidic aqueous solution of the metallic elementsin the mole ratios given in the formula, neutralizing the aqueoussolution to provide a suspenion of hydroxides of the metallic elements,subjecting the suspension in an autoclave under pressure to atemperature between 150° and 330° C. for time sufficient to produceprecipitate of the composition and of an average particle size between0.02 and 0.2 micron in a mother liquor, and separating the precipitatefrom the mother liquor.

[0025] U.S. Pat. No. 5,727,385 (Hepburn '385) discloses a catalystsystem, located in the exhaust gas passage of a lean-burn internalcombustion engine, useful for converting carbon monoxide, nitrogenoxides, and hydrocarbons present in nitrogen oxide catalyst being atransition metal selected from the group consisting of cooper, chromium,iron cobalt, nickel, iridium, cadmium, silver, gold platinum, maganese,and mixtures thereof loaded on a refractory oxide or exchanged intozeolite; an (2) a nitrogen oxide (NOx) trap material which absords NOxwhen the exhaust gas flowing into the trap material is lean and releasesthe absords NOx when the concentration of oxygen in the inflowingexhaust gas is lowered. The nitrogen oxide trap material is locateddownstream of the lean-burn nitrogen oxide catalyst in the exhaust gaspassage such that the exhaust gases are exposed to the lean-burncatalyst prior to being exposed to the nitrogen oxide trap material.

[0026] U.S. Pat. No. 5,750,082 (Hepburn et al. '082) discloses anitrogen oxide trap useful for tapping nitrogen oxide present in theexhaust gases generated during lean-burn operation of an internalcombustion engine. The trap comprises distinct catalyst phases: (a) aporous support loaded with catalyst comprising 0.1 to 5 weight %platinum; and (b) another porous support loaded with 2 to 30 weight %catalyst of an alkaline metal material selected from the groupconsisting of alkali metal elements and alkaline earth elements.

[0027] U.S. Pat. No. 5,753,192 (Dobson et al.) discloses a nitrogenoxide trap useful for trapping nitrogen oxide present in an exhaust gasstream generated during lean-burn operation of an internal combustion ofthe exhaust gas is lowered. The trap comprises a porous support loadedmetal selected from platinum, palladium, rhodium and mixtures thereof;(b) 3.5-15 wt. % zirconium; and (c) 15-30 wt. % sulfate.

[0028] U.S. Pat. No. 5,758,489 (Hepburn et al. '489) discloses anitrogen oxide trap useful for trapping nitrogen oxide present in theexhaust gases generated during lean burn operation of an internalcombustion engine. The trap comprises a porous support; and catalystscomprising at least 10 weight percent lithium and 0.2 to 4 weightpercent platinum loaded on the porous support.

[0029] U.S. Pat. No. 5,759,553 (Lott et al.) discloses a NOx adsorbermaterial comprising an activated alkali metal-doped and copper-dopedhydrous zirconium oxide material that adsords NOx in an oxidizingatomosphere and desorbs NOx in a non-oxidizing atomosphere.

[0030] U.S. Pat. No. 5,910,097 (Boegner et al.) discloses an exhaustemission control system for an internal combustion engine. The systemcomprises two absorber parts arranged in parallel for alternateadsorption and desorption of nitrogen oxides contained in an exhaustfrom an engine. A means for conducting the exhaust further downstream isprovided emerging from one of the two absorber parts currently operatedin the adsorption mode and for recycling the exhaust emerging from theother of the two adsorber parts operating in the desorption mode into anintake line of the engine. An oxidizing converter is located near theengine and upstream from the adsorber parts for oxidation of at least NOcontained in the exhaust to NO₂. An exhaust line section is locatedupstream of the adsorber parts and is divided into a main line branchand a partial line branch parallel to the main line branch. The twoadsorber parts are connected by control valves to the main line branchand the partial line branch such that the one adsorber part that isoperating in the adsorption mode is fed by the exhaust stream from themain line branch and the other adsorber part that is operating in thedesorption mode is supplied by the exhaust stream from partial linebranch.

[0031] European patent application 589,393A2 discloses a method forpurifying and oxygen rich exhaust gas by simultaneously removing thecarbon monoxide, hydrocarbons, and nitrogen oxides contained in theexhaust gas. The method comprises bringing the oxygen rich exhaust gasinto contact with an exhaust gas purifying catalyst comprised of (i) atleast one noble metal selected from the group consisting of platinum andpalladium (ii) barium, and (iii) at least one metal selected from thegroup consisting of alkali metals, iron, nickel, cobalt, and magnesium,supported on a carrier coposed of a porous substance.

[0032] European patent application 669,157A1 discloses a catalyst forpurifying exhaust gases. The catalyst comprises a heat resistantsupport; a porous layer coated on the heat resistant support; a noblemetal catalyst ingredient laode on the porous layer; and an NOx storagecomponent selected from the group consisting of alkaline-earth metals,rare-earth elements and alkali metals, and loaded on the porous layer.The noble metal catalyst ingredient and the NOx storage component aredisposed adjacent to each other, and dispersed uniformly in the porouslayer.

[0033] European patent application 764,459A2 discloses a nitrogen oxidetrap useful for trapping nitrogen oxide present in the exhaust gasesgenerated during lean-burn operation of an internal combustion engine.The trap comprises distinct catalyst phases (a) a first porous supportloaded with catalyst comprising 0.1 to 5 weight % platinum; and (b) asecond porous support loaded with 2 to 30 weight % catalyst of amaterial selected from the group consisting of alkali metal elements andalkaline earth elements.

[0034] European patent application 764,460A2 discloses a nitrogen oxidetrap useful for trapping nitrogen oxide present in the exhaust gasesgenerated during lean-burn operation of an internal combustion engine.The trap comprises a porous support; and catalysts consisting ofmanganese and potassium loaded on the porous support.

[0035] Laboratory and engine tests were carried out to describe thesulfur effect on the NOx adsorbers catalysts efficiency for gasolinelean burn engines. One aspect of the study dealt with the NOx storageefficiency of the adsorber under laboratory conditions, especiallyregarding the SO2 gas phase concentration. The rate of sulfur storing isgreatly affected by the SO2 gas concentration. While 6.5 hours arerequired to go from 70% NOx reduction to only 35% when the gas mixturecontains 10 ppm SOx, it takes 20 hours with 5 ppm of SOx and more than60 hours with a 2 ppm SO2 condition. The relationship between the lossin NOx trap performance and SO2 concentration appears to have anexponential shape. The same amount of sulfur (0.8% mass) is depositedonto the catalyst within 10 hours with the feed gas containing 10 ppm ofSO2 and within 50 hours with 2 ppm SO2. Nevertheless, it was shown thatthe loss in NOx-trap efficiency is not the same in these two cases. Theefficiency decreased from 70% to 25% in the first case (with 10 ppm SO2)and from 70% to only 38% in the second case (with 2 ppm SO2). The secondaspect describes a parametric study on engine bench concerning thesulfur effect on NOx trap efficiency and the required conditions(temperature, air/fuel ratio) to obtain different rates of desulfation.For instance, after 70 hours, NOx efficiency decreased from 90% to 25%with a sulfur content in gasoline of 110 ppm. Complete regenerationrequires various durations of desulfation depending on air/fuel ratio(lambda=1 to 0.95) and temperature conditions (950 to 750° C.). Forexample, complete regeneration occurs after several minutes at lambda=1and several sets of ten seconds at lambda=0.95 at 650° C. Results showthat sulfur content close to EURO III gasoline standards is the mainobstacle for the introduction of NOx adsorber catalyst in Europe. Impactof Sulfur on NOx Trap Catalyst Activity Study of the RegenerationConditions, M. Guyon et al., Society of Automotive Engineers, 982607(1998).

[0036] The conventional catalysts described above employing NO_(x)storage components have the disadvantage under practical applications ofsuffering from long-term activity loss because of SO_(x) poisoning ofthe NO_(x) traps. The conventional NO_(x) trap components employed inthe catalysts tend to trap SO_(x) and form very stable sulfates whichrequire regeneration at 650° C. which is not practical for lowtemperature diesel exhaust. Accordingly, it is a continuing goal todevelop NOx trap catalysts which can reversibly trap SO_(x) present inthe gaseous stream and thereby prevent SO_(x) sulfur oxide poisoning ofthe NO_(x) trap and can be regenerated at moderate temperatures withrich pulses, rather than at high temperatures.

SUMMARY OF THE INVENTION

[0037] The present invention pertains to a method for removing NO_(x)contaminants from a SOx containing gaseous stream comprising the stepsof:

[0038] (1) providing a catalyst composite;

[0039] (2) in a sorbing period, passing a lean gaseous stream comprisingNO_(x) and SO_(x) within a sorbing temperature range through thecatalyst composite to sorb at least some of the NO_(x) contaminants andthereby provide a NO_(x) depleted gaseous stream exiting the catalystcomposite and to sorb and abate at least some of the SO_(x) contaminantsin the gaseous stream and thereby provide a SO_(x) depleted gaseousstream exiting the catalyst composite;

[0040] (3) in a NO_(x) desorbing and abating period, changing the leangaseous stream to a rich gaseous stream to thereby reduce and desorb atleast some of the NO_(x) contaminants from the catalyst composite andthereby provide a reduced NO_(x) enriched gaseous stream exiting thecatalyst composite;

[0041] (4) in a SOx desorbing period, changing the lean gaseous streamto a rich gaseous stream and raising the temperature of the gaseousstream to within a desorbing temperature range to thereby reduce anddesorb at least some of the SO_(x) contaminants from the catalystcomposite and thereby regenerate the catalyst composite and provide areduced SO_(x) enriched gaseous stream exiting the catalyst composite;and wherein the catalyst composite comprises:

[0042] (a) a platinum component;

[0043] (b) a support; and

[0044] (c) a NOx sorbent component comprising a first metal oxide and asecond metal oxide, wherein the metal in the first metal oxide isselected from the group consisting of aluminum, titanium, zirconium,silicon, and composites thereof, and the metal in the second metal oxideis selected from the group consisting of Group IIA metals, Group IIImetals, Group IV metals, rare earth metals, and transition metals;wherein the metal in the first metal oxide is different from the metalin the second metal oxide;

[0045] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0046] (i) providing an aqueous suspension or solution of the first andsecond metal oxides, or precursors thereof, or both, wherein theprecursors of the first and second metal oxides are metal salts whichwhen hydrolyzed produce the respective metal oxides;

[0047] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0048] (iii) separating the precipitate from the mother liquor.

[0049] The present invention also pertains to a catalyst compositeprepared by a hydrothermal synthesis method which comprises the stepsof:

[0050] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0051] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0052] (iii) separating the precipitate from the mother liquor; and

[0053] (iv) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0054] The present invention also pertains to a method of forming acatalyst composite which comprises the steps of:

[0055] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0056] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0057] (iii) separating the precipitate from the mother liquor; and

[0058] (iv) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0059] The present invention also pertains to a method of forming acatalyst composite which comprises the steps of:

[0060] (1) forming an admixture of:

[0061] (a) a support; and

[0062] (b) a NOx sorbent component;

[0063] (2) combining a water-soluble or dispersible platinum componentand the admixture from step (1) with an aqueous liquid to form asolution or dispersion which is sufficiently dry to absorb essentiallyall of the liquid;

[0064] (3) forming a layer of the solution or dispersion on a substrate;and

[0065] (4) converting the platinum component in the resulting layer to awater-insoluble form;

[0066] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0067] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0068] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0069] (iii) separating the precipitate from the mother liquor.

[0070] The sulfur tolerant NOx trap catalyst composites are highlyeffective with a sulfur containing fuel by trapping sulfur oxidecontaminants in lean when conventional NOx trap catalysts tend to bepoisoned, and release sulfur oxide contaminants in rich to regeneratethe NOx trap. The sulfur tolerant NOx trap catalyst composites areparticularly suitable for diesel engines because the composites can beregenerated at moderate temperatures with rich pulses, rather than athigh temperatures.

[0071] In a preferred embodiment, the present invention pertains to amethod for removing NO_(x) contaminants from a SOx containing gaseousstream comprising the steps of:

[0072] (1) providing a catalyst composite;

[0073] (2) in a sorbing period, passing a lean gaseous stream comprisingNO_(x) and SO_(x) within a sorbing temperature range through thecatalyst composite to sorb at least some of the NO_(x) contaminants andthereby provide a NO_(x) depleted gaseous stream exiting the catalystcomposite and to sorb and abate at least some of the SO_(x) contaminantsin the gaseous stream and thereby provide a SO_(x) depleted gaseousstream exiting the catalyst composite;

[0074] (3) in a NO_(x) desorbing and abating period, changing the leangaseous stream to a rich gaseous stream to thereby reduce and desorb atleast some of the NO_(x) contaminants from the catalyst composite andthereby provide a reduced NO_(x) enriched gaseous stream exiting thecatalyst composite;

[0075] (4) in a SO_(x) desorbing period, changing the lean gaseousstream to a rich gaseous stream and raising the temperature of thegaseous stream to within a desorbing temperature range to thereby reduceand desorb at least some of the SO_(x) contaminants from the catalystcomposite and thereby regenerate the catalyst composite and provide areduced SO_(x) enriched gaseous stream exiting the catalyst composite;and wherein the catalyst composite comprises:

[0076] (a) a platinum component;

[0077] (b) a support; and

[0078] (c) a NOx sorbent component comprising the followingconstituents:

[0079] (i) Na₂O in an amount up to about 0.1%;

[0080] (ii) MgO in an amount up to about 1%;

[0081] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0082] (iv) SrO in an amount from about 0.5% to about 15%;

[0083] (v) Y₂O₃ in an amount up to about 5%; and

[0084] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0085] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0086] (i) providing an aqueous suspension or solution of theconstituents of the NOx sorbent component;

[0087] (ii) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0088] (iii) separating the precipitate from the mother liquor.

[0089] In another preferred embodiment, the present invention pertainsto a catalyst composite prepared by a hydrothermal synthesis methodwhich comprises the steps of:

[0090] (a) providing an aqueous suspension or solution of a NOx sorbentcomponent comprising the following constituents:

[0091] (i) Na₂O in an amount up to about 0.1%;

[0092] (ii) MgO in an amount up to about 1%;

[0093] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0094] (iv) SrO in an amount from about 0.5% to about 15%;

[0095] (v) Y₂O₃ in an amount up to about 5%; and

[0096] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0097] (b) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0098] (c) separating the precipitate from the mother liquor; and

[0099] (d) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0100] In another preferred embodiment, the present invention pertainsto a method of forming a catalyst composite which comprises the stepsof:

[0101] (a) providing an aqueous suspension or solution of a NOx sorbentcomponent comprising the following constituents:

[0102] (i) Na₂O in an amount up to about 0.1%;

[0103] (ii) MgO in an amount up to about 1%;

[0104] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0105] (iv) SrO in an amount from about 0.5% to about 15%;

[0106] (v) Y₂O₃ in an amount up to about 5%; and

[0107] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0108] (b) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0109] (c) separating the precipitate from the mother liquor; and

[0110] (d) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0111] In another preferred embodiment, the present invention pertainsto a method of forming a catalyst composite which comprises the stepsof:

[0112] (1) forming an admixture of:

[0113] (a) a support; and

[0114] (b) a NOx sorbent component comprising the followingconstituents:

[0115] (i) Na₂O in an amount up to about 0.1%;

[0116] (ii) MgO in an amount up to about 1%;

[0117] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0118] (iv) SrO in an amount from about 0.5% to about 15%;

[0119] (V) Y₂O₃ in an amount up to about 5%; and

[0120] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0121] (2) combining a water-soluble or dispersible platinum componentand the admixture from step (1) with an aqueous liquid to form asolution or dispersion which is sufficiently dry to absorb essentiallyall of the liquid;

[0122] (3) forming a layer of the solution or dispersion on a substrate;and

[0123] (4) converting the platinum component in the resulting layer to awater-insoluble form;

[0124] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0125] (i) providing an aqueous suspension or solution of theconstituents of the NOx sorbent component;

[0126] (ii) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0127] (iii) separating the precipitate from the mother liquor.

[0128] The preferred NOx sorbent component may further comprise BaO inan amount from about 0.5% to about 15%.

DETAILED DESCRIPTION OF THE INVENTION AND SPECIFIC EMBODIMENTS THEREOF

[0129] The present invention relates to sulfur tolerant catalystcomposites useful for reducing contaminants in exhaust gas streams,especially gaseous streams containing sulfur oxide contaminants. Morespecifically, the present invention is concerned with improved NOx trapcatalysts for use in diesel engines as well as lean burn gasolineengines. The sulfur tolerant NOx trap catalyst composites comprise aplatinum component, a support, and a NOx sorbent component prepared byhydrothermal synthesis. The NOx sorbent component comprises a firstmetal oxide and a second metal oxide. The metal in the first metal oxideis selected from the group consisting of aluminum, titanium, zirconium,silicon, and composites thereof, and the metal in the second metal oxideis selected from the group consisting of Group IIA metals, Group IIImetals, Group IV metals, rare earth metals, and transition metals. Themetal in the first metal oxide is different from the metal in the secondmetal oxide. The sulfur tolerant NOx trap catalyst composites are highlyeffective with a sulfur containing fuel by trapping sulfur oxidecontaminants which tend to poison conventional NOx trap catalysts usedto abate other pollutants in the stream. The sulfur tolerant NOx trapcatalyst composites are suitable for diesel engines because thecomposites can be regenerated at moderate temperatures with rich pulses,rather than at high temperatures. Conventional NOx trap catalysts arereadily poisoned by sulfur and cannot be regenerated by rich pulsesbelow 650° C. Since the exhaust temperature of diesel engines is low,the temperature requirement of 650° C. for regeneration and higher isnot practical. The sulfur tolerant NOx trap catalyst composites of thepresent invention can be regenerated with rich pulses at moderatetemperatures (550° C. or lower). Applicants believe that when the NOxsorbent components of the present invention are prepared by hydrothermalsynthesis, the resulting NOx sorbent components are fine crystallinepowders having sufficiently small average particle sizes(microparticles) such that the NOx sorbent components regenerate (desorbSOx) faster than NOx sorbent components not prepared by hydrothermalsynthesis.

[0130] The improved NOx trap catalysts are sulfur tolerant and can beemployed in a lean/rich environment containing sulfur for an extendedperiod of time. Accumulated sulfur in the NOx trap catalysts canthereafter be released at a temperature that is easily reachable underthe engine operation conditions, for example, 550° C. or lower. Thus,the NOx trap catalysts can be used in a sulfur containing environmentcontinuously provided they are regenerated periodically. If sulfur canbe released under normal engine working conditions, then sulfur isautomatically being regenerated without additional efforts and the NOxtrap catalyst becomes a truly sulfur resistant NOx trap.

[0131] The NOx trap materials of the present invention are generated bya hydrothermal synthesis process so as to yield ultra fine sub-micronmixed oxide composites. While not wishing to be held to a mechanism, itis believed that ultra fine sub-micron mixed oxides are more active thanthe large, greater than 1 micron size, bulk phase materials that areproduced by conventional processes. It is further believed that thereductant can more effectively clean the surface to regenerate newadsorption sites, onto which nitrates and sulfates adsorb and the bulkoxide takes longer to regenerate because of diffusion limitation in therapid regeneration needed. On a diesel engine, a bulk NOx trap compositecan not be fully ‘scrubbed’ of sulfur in the short regeneration cycle.Therefore, it becomes quickly poisoned. Conversely, the oxides producedfrom the hydrothermal method regenerate more effectively.

[0132] A fresh SOx trap should clear SOx before it reaches the NOx traplocated downstream. However, any SOx trap has limited capacity. Manyproblems exist when a separated SOx trap is used together with a NOxtrap. A higher temperature is needed to regenerate the SOx trap, thereleased SOx in the gas flow must be avoided to poison the NOx trap thatis located down stream, engine management becomes more complicated, andthe pollutant abatement system becomes complicated. The presentinvention provides a trap that not only traps NOx and SOx but alsoreleases SOx when NOx is released during the NOx regeneration so thatsome sites that have been trapping SOx are also regenerated at the sametime. In other words, the SOx tolerant NOx trap may not require a highertemperature to be regenerated after being sulfated in the SOxenvironment. As an option, a separate SOx trap is not needed, the NOxand SOx trap may be combined. A lean burn or diesel catalyst equippedwith a NOx/SOx trap can be regenerated similar to regenerating a simpleNOx trap in a sulfur free environment.

[0133] With the SOx tolerant NOx trap of the present invention, one mayoperate the pollutant abating system without the need of a highertemperature for SOx desorbing, and/or a separate SOx desorbing period.The SOx tolerant NOx trap can also work continuously at a moderatetemperate (e.g. 300° C.) without raising the temperature for trapregeneration (only lean/rich alternative required).

[0134] The present invention includes a method of making SOx tolerantNOx traps through the selection of the right mixed oxides prepared byhydrothermal synthesis. After being sulfated, the SOx tolerant NOx trapcan be fully regenerated at a temperature as low as 400° C. Barium oxidetype NOx traps cannot be regenerated at such a low temperature. Afterbeing extensively sulfated for a continuous 68 hours (the amount of SOxpassed through equaled the same amount of the trap material), the NOxconversion was still effective. The SOx tolerant NOx trap workedeffectively without any temperature rising for trap regeneration (onlylean/rich alternative required).

[0135] A catalyst adsorbs or traps NOx when the exhaust gas is lean andreleases the stored NOx when the exhaust stream is rich. The releasedNOx is subsequently reduced to N₂ over the same catalyst. The richenvironment in a diesel engine is normally realized with a rich pulsegenerated by either engine management or injection of reducing agents(such as fuel, or a CO or CO/H₂ mixture) into the exhaust pipe. Thetiming and frequency of the rich pulse is determined by the NOx levelemitted from the engine, the richness of the exhaust, or theconcentration of the reductant in the rich pulse and the NOx conversiondesired. Normally, the longer the lean period, the longer the rich pulseis needed. The need for longer rich pulse timing may be compensated byhigher concentration of the reductant in the pulse. Overall, thequantity of the NOx trapped by the NOx trap should be balanced by thequantity of the reductant in the rich pulse. The lean NOx trapping andrich NOx trap regeneration are operative at normal diesel operatingtemperatures (150-450° C.). Beyond this temperature window, theefficiency of the NOx trap catalyst becomes less effective. In a sulfurcontaining exhaust stream, the catalyst becomes deactivated over timedue to sulfur poisoning. To regenerate the sulfur-poisoned NOx trap, arich pulse (or pulses) must be applied at temperatures higher than thenormal diesel operating temperature. The regeneration time of thegeneration depends on the sulfur level in the exhaust (or fuel sulfurlevel) and the length of the catalyst had exposed to thesulfur-containing stream. The quantity of the reductant added during thedesulfation should counterbalance the total amount of sulfur trapped inthe catalyst. Engine operability will determine whether a single longpulse or multiple short pulses are employed.

[0136] As used herein, the following terms, whether used in singular orplural form, have the meaning defined below.

[0137] The term “catalytic metal component”, or “platinum metalcomponent”, or reference to a metal or metals comprising the same, meansa catalytically effective form of the metal or metals, whether the metalor metals are present in elemental form, or as an alloy or a compound,e.g., an oxide.

[0138] The term “component” or “components” as applied to NO_(x)sorbents means any effective NO_(x)-trapping forms of the metals, e.g.,oxygenated metal compounds such as metal hydroxides, mixed metal oxides,metal oxides or metal carbonates.

[0139] The term “composite” means bimetallic or multi-metallic oxygencompounds, such as Ba₂SrWO₆, which are true compounds as well asphysical mixtures of two or more individual metal oxides, such as amixture of SrO and BaO.

[0140] The term “dispersed”, when applied to a component dispersed ontoa bulk support material, means immersing the bulk support material intoa solution or other liquid suspension of the component or a precursorthereof. For example, the sorbent strontium oxide may be dispersed ontoan alumina support material by soaking bulk alumina in a solution ofstrontium nitrate (a precursor of strontia), drying the soaked aluminaparticles, and heating the particles, e.g., in air at a temperature fromabout 450° C. to about 750° C. (calcining) to convert the strontiumnitrate to strontium oxide dispersed on the alumina support materials.

[0141] The term “gaseous stream” or “exhaust gas stream” means a streamof gaseous constituents, such as the exhaust of an internal combustionengine, which may contain entrained non-gaseous components such asliquid droplets, solid particulates, and the like.

[0142] The terms “g/in³” or “g/ft3” are used to describe weight pervolume units describe the weight of a component per volume of catalystor trap member including the volume attributed to void spaces such asgas-flow passages.

[0143] The term “lean” mode or operation of treatment means that thegaseous stream being treated contains more oxygen that thestoichiometric amount of oxygen needed to oxidize the entire reductantscontent, e.g., HC, CO and H₂, of the gaseous stream.

[0144] The term “platinum group metals” means platinum, rhodium,palladium, ruthenium, iridium, and osmium.

[0145] The term “sorb” means to effect sorption.

[0146] The term “stoichiometric/rich” mode or operation of treatmentmeans that the gaseous stream being treated refers collectively to thestoichiometric and rich operating conditions of the gas stream.

[0147] The term “washcoat” has its usual meaning in the art of a thin,adherent coating of a catalytic or other material applied to arefractory carrier material, such as a honeycomb-type carrier member,which is sufficiently porous to permit the passage there through of thegas stream being treated.

[0148] In accord with the present invention, a method is provided forremoving NO_(x) contaminants from a SOx containing gaseous stream. Themethod comprises (1) providing a catalyst composite; (2) in a sorbingperiod, passing a lean gaseous stream comprising NO_(x) and SO_(x)within a sorbing temperature range through the catalyst composite tosorb at least some of the NO_(x) contaminants and thereby provide aNO_(x) depleted gaseous stream exiting the catalyst composite and tosorb and abate at least some of the SO_(x) contaminants in the gaseousstream and thereby provide a SO_(x) depleted gaseous stream exiting thecatalyst composite; (3) in a NO_(x) desorbing and abating period,changing the lean gaseous stream to a rich gaseous stream to therebyreduce and desorb at least some of the NO_(x) contaminants from thecatalyst composite and thereby provide a reduced NO_(x) enriched gaseousstream exiting the catalyst composite; (4) in a SO_(x) desorbing period,changing the lean gaseous stream to a rich gaseous stream and raisingthe temperature of the gaseous stream to within a desorbing temperaturerange to thereby reduce and desorb at least some of the SO_(x)contaminants from the catalyst composite and thereby regenerate thecatalyst composite and provide a reduced SO_(x) enriched gaseous streamexiting the catalyst composite. The catalyst composite comprises (a) aplatinum component; (b) a support; and (c) a NOx sorbent componentcomprising a first metal oxide and a second metal oxide, wherein themetal in the first metal oxide is selected from the group consisting ofaluminum, titanium, zirconium, silicon, and composites thereof, and themetal in the second metal oxide is selected from the group consisting ofGroup IIA metals, Group III metals, Group IV metals, rare earth metals,and transition metals; wherein the metal in the first metal oxide isdifferent from the metal in the second metal oxide. The NOx sorbentcomponent is prepared by a hydrothermal synthesis process comprising thesteps of (i) providing an aqueous suspension or solution of the firstand second metal oxides, or precursors thereof, or both, wherein theprecursors of the first and second metal oxides are metal salts whichwhen hydrolyzed produce the respective metal oxides; (ii) subjecting thesuspension or solution of the first and second metal oxides, orprecursors thereof, to a temperature from about 150° C. to about 300° C.in an autoclave under pressure for a time sufficient to produce aprecipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and (iii) separating the precipitate fromthe mother liquor.

[0149] In general, the SOx desorbing temperature range is greater thanabout 300° C., preferably, the desorbing temperature range is greaterthan about 350° C., more preferably, the desorbing temperature range isgreater than about 400° C., and most preferably the desorbingtemperature range is greater than about 450° C. The SOx desorbingtemperature may also be greater than about 500° C., preferably greaterthan about 550° C., more preferably greater than about 600° C., and mostpreferably greater than about 650° C.

[0150] As set out above, the sulfur tolerant catalyst composite of thepresent invention includes a platinum component, and optionally aplatinum group metal component other than platinum. The optionalplatinum group metal component other than platinum may be selected fromthe group consisting of palladium, rhodium, ruthenium, iridium, andosmium components. The preferred platinum group metal component otherthan platinum is selected from the group consisting of palladium,rhodium, and mixtures thereof.

[0151] The sulfur tolerant catalyst composite of the present inventionalso includes a support made of a high surface area refractory oxidesupport. The support may be selected from the group consisting ofalumina, silica, titania, and zirconia compounds. Useful high surfacearea supports include one or more refractory oxides. These oxidesinclude, for example, silica and metal oxides such as alumina, includingmixed oxide forms such as silica-alumina, aluminosilicates which may beamorphous or crystalline, alumina-zirconia, alumina-chromia,alumina-ceria and the like. Preferably the support is an activatedcompound selected from the group consisting of activated alumina,alumina-ceria, alumina-chromia, alumina-silica, alumina-zirconia,silica, silica-titania, silica-titania-alumina, silica-titania-zirconia,titania, zirconia, zirconia-titania, and zirconia-alumina-titania.Desirably, the active alumina has a specific surface area of 60 to 300m²/g.

[0152] The sulfur tolerant catalyst composite of the present inventionalso includes a NO_(x) sorbent component. The NOx sorbent componentcomprises a first metal oxide and a second metal oxide. The metal in thefirst metal oxide is selected from the group consisting of aluminum,titanium, zirconium, silicon, and composites thereof. The metal in thesecond metal oxide is selected from the group consisting of Group IIAmetals, Group III metals, Group IV metals, rare earth metals, andtransition metals. The metal in the first metal oxide is different fromthe metal in the second metal oxide. Preferably, the metal in the secondmetal oxide is selected from the group consisting of magnesium, calcium,strontium, barium, scandium, titanium, zirconium, hafnium, lanthanum,cerium, praseodymium, neodymium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, and zinc. Morepreferably, the metal in the second metal oxide is selected from thegroup consisting of barium, lanthanum, cerium, iron, cobalt, and copper.In a specific embodiment, the metals in the first and second metaloxides are selected from the group consisting of aluminum/cerium/barium,aluminum/copper/lanthanum, aluminum/cobalt/lanthanum, and iron/aluminum.

[0153] As set out above, the NOx sorbent component is prepared by ahydrothermal synthesis process which employs an aqueous suspension orsolution of the first and second metal oxides, or precursors thereof, orboth. The precursors of the first and second metal oxides are metalsalts when hydrolyzed produce the respective metal oxides. Preferredprecursors of the first metal oxide and second metal oxide arewater-soluble/dispersible metal salts selected from the group consistingof acetates, nitrates, hydroxides, oxychlorides, hydroxychlorides,carbonates, sulfates, oxalates, and tartrates.

[0154] The metal in the first metal oxide and the metal in the secondmetal oxide are preferably present in a ratio from about 3:7 to about9:1, more preferably from about 4:6 to about 8.5:1.5, respectively, andmost preferably from about 5:5 to about 7.5:2.5, respectively.

[0155] As set out above, the NOx sorbent component is prepared byhydrothermal synthesis. In general, the process comprises the steps of(i) providing an aqueous suspension or solution of the at least 2 metaloxides, or precursors thereof, wherein the precursors of the at least 2metal oxides are metal salts which when hydrolyzed produce therespective metal oxides; (ii) subjecting the suspension or solution ofthe at least 2 metal oxides, or precursors thereof, to a temperaturefrom about 150° C. to about 300° C. in an autoclave under pressure for atime sufficient to produce a precipitate having an average particle sizefrom about 0.001 to about 0.2 micron in a mother liquor; and (iii)separating the precipitate from the mother liquor.

[0156] The suspension of metal hydroxides is preferably subjected to atemperature from about 175° C. to about 250° C., preferably from about185° C. to about 240° C. The precipitate preferably has an averageparticle size from about 0.01 to about 0.2 micron, preferably from about0.05 to about 0.15 micron.

[0157] In a preferred embodiment, the catalyst composite comprises (i)at least about 1 g/ft³ of the platinum component; (ii) from about 0.15g/in³ to about 6.0 g/in³ of the support; and (iii) from about 0.025g/in³ to about 4 g/in³ of the NO_(x) sorbent component.

[0158] The catalyst composite may be supported on a metal or ceramichoneycomb carrier or is self-compressed.

[0159] The NOx sorbent component may further comprise a third metaloxide, wherein the metal in the third metal oxide is selected from thegroup consisting of aluminum, titanium, zirconium, silicon, andcomposites thereof, and the metal in the second metal oxide is selectedfrom the group consisting of Group IIA metals, Group III metals, GroupIV metals, rare earth metals, and transition metals. In this embodiment,the metal in the third metal oxide is different from the metal in thefirst and second metal oxides.

[0160] In accordance with the present invention, NOx sorbent componentsare prepared by hydrothermal synthesis to yield fine powders. Ingeneral, the NOx sorbent components are prepared by providing an aqueoussuspension or solution of the first and second metal oxides, orprecursors thereof, or both, subjecting the suspension or solution ofthe first and second metal oxides, or precursors thereof, to atemperature from about 150° C. to about 300° C. in an autoclave underpressure for a time sufficient to produce a precipitate having anaverage particle size from about 0.001 to about 0.2 micron in a motherliquor, and separating the precipitate from the mother liquor.

[0161] The precursor solution/suspension is subsequently subjected tohydrothermal reaction with stirring to provide a fine precipitate. Thereaction may be carried out in an autoclave, which is preferably made ofstainless steel coated with heat-resistant high polymer, such aspolytetrafluoroethylene. The precipitate produced by the hydrothermalreaction at a temperature from about 150° C. to about 300° C. generallyhas an average particle size between 0.001 and 0.2 micron. Theprecipitate may be separated from the mother liquor by filtration, thenwashed and dried.

[0162] In a preferred embodiment, the NOx sorbent component is preparedby a process comprising the steps of (i) providing an aqueous suspensionor solution of the at least 2 metal oxides, or precursors thereof, orboth, wherein the precursors of the at least 2 metal oxides are metalsalts which when hydrolyzed produce the respective metal oxides; (ii)subjecting the suspension or solution of the at least 2 metal oxides, orprecursors thereof, to a temperature from about 150° C. to about 300° C.in an autoclave under pressure for a time sufficient to produce aprecipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and (iii) separating the precipitate fromthe mother liquor.

[0163] In use, the exhaust gas stream, comprising air, water,hydrocarbons, carbon monoxide, nitrogen oxides, and sulfur oxides andwhich is contacted with the catalyst composite of the present invention,is alternately adjusted between lean and stoichiometric/rich operatingconditions so as to provide alternating lean operating periods andstoichiometric/rich operating periods. The exhaust gas stream beingtreated may be selectively rendered lean or stoichiometric/rich eitherby adjusting the air-to-fuel ratio fed to the engine generating theexhaust or by periodically injecting a reductant into the gas streamupstream of the catalyst. For example, the catalyst composite of thepresent invention is well suited to treat the exhaust of engines,especially diesel engines, which continuously run lean. In a dieselengine, in order to establish a stoichiometric/rich operating period, asuitable reductant, such as fuel, may be periodically sprayed into theexhaust immediately upstream of the catalytic trap of the presentinvention to provide at least local (at the catalytic trap)stoichiometric/rich conditions at selected intervals. Partial lean-bumengines, such as partial lean-bum gasoline engines, are designed withcontrols which cause them to operate lean with brief, intermittent richor stoichiometric conditions. In practice, the sulfur tolerant NOx trapcatalyst composite absorbs in-coming SO_(x) during a lean mode operation(100° C. to 500° C.) and desorbs SO_(x) (regenerate) during a rich modeoperation (greater than about 300° C., preferably greater than about350° C., more preferably greater than about 400° C., and most preferablygreater than about 450° C. The SOx desorbing temperature may also begreater than about 500° C., preferably greater than about 550° C., morepreferably greater than about 600° C., and most preferably greater thanabout 650° C. When the exhaust gas temperature returns to a lean modeoperation (100° C. to 500° C.), the regenerated sulfur tolerant NOx trapcatalyst composite will again selectively absorb in-coming SO_(x). Theduration of the lean mode may be controlled so that the sulfur tolerantNOx trap catalyst composite will not be saturated with SO_(x).

[0164] When the composition is applied as a thin coating to a monolithiccarrier substrate, the proportions of ingredients are conventionallyexpressed as grams of material per cubic inch (g/in³) of the catalystand the substrate. This measure accommodates different gas flow passagecell sizes in different monolithic carrier substrates. Platinum groupmetal components are based on the weight of the platinum group metal.

[0165] A useful and preferred sulfur tolerant NOx trap catalystcomposite has at least about 1 g/ft³ of a platinum component; from about0.15 g/in³ to about 4.0 g/in³ of a support; at least about 1 g/ft³ of aplatinum group metal component other than platinum; from about 0.025g/in³ to about 4 g/in³ of a NO_(x) sorbent component.

[0166] The specific construction of the catalyst composite set out aboveresults in an effective catalyst that reversibly traps sulfur oxidecontaminants present and thereby prevents the sulfur oxide contaminantsfrom poisoning the NOx trap catalysts for use in diesel engines. Thecatalyst composite can be in the form of a self-supported article suchas a pellet, and more preferably, the sulfur tolerant NOx trap catalystcomposite is supported on a carrier, also referred to as a substrate,preferably a honeycomb substrate. A typical so-called honeycomb-typecarrier member comprises a material such as cordierite or the like,having a plurality of fine, gas-flow passages extending from the frontportion to the rear portion of the carrier member. These fine gas-flowpassages, which may number from about 100 to 900 passages or cells persquare inch of face area (“cpsi”), have a catalytic trap material coatedon the walls thereof.

[0167] The present invention also includes a method for treating anexhaust gas stream which comprises the step of contacting the gas streamcomprising carbon monoxide and/or hydrocarbons, nitrogen oxides, andsulfur oxides with the catalyst composite set out above. The presentinvention also includes a method of treating an exhaust gas streamcomprising the steps of contacting the stream with the catalystcomposite set out above under alternating periods of lean andstoichiometric or rich operation. Contacting is carried out underconditions whereby at least some of the SO_(x) in the exhaust gas streamis trapped in the catalytic material during the periods of leanoperation and is released and reduced during the periods ofstoichiometric or rich operation.

[0168] In a specific embodiment, the present invention pertains to acatalyst composite prepared by a hydrothermal synthesis method whichcomprises the steps of:

[0169] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0170] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0171] (iii) separating the precipitate from the mother liquor; and

[0172] (iv) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0173] The present invention also pertains to a method of forming acatalyst composite which comprises the steps of:

[0174] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0175] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0176] (iii) separating the precipitate from the mother liquor; and

[0177] (iv) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0178] The present invention also pertains to a method of forming acatalyst composite which comprises the steps of:

[0179] (1) forming an admixture of:

[0180] (a) a support; and

[0181] (b) a NOx sorbent component;

[0182] (2) combining a water-soluble or dispersible platinum componentand the admixture from step (1) with an aqueous liquid to form asolution or dispersion which is sufficiently dry to absorb essentiallyall of the liquid;

[0183] (3) forming a layer of the solution or dispersion on a substrate;and

[0184] (4) converting the platinum component in the resulting layer to awater-insoluble form;

[0185] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0186] (i) providing an aqueous suspension or solution of a first metaloxide and a second metal oxide, or precursors thereof, or both, whereinthe precursors of the first and second metal oxides are metal saltswhich when hydrolyzed produce the respective metal oxides;

[0187] (ii) subjecting the suspension or solution of the first andsecond metal oxides, or precursors thereof, to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and

[0188] (iii) separating the precipitate from the mother liquor.

[0189] The sulfur tolerant NOx trap catalyst composites are highlyeffective with a sulfur containing fuel by trapping sulfur oxidecontaminants which tend to poison conventional NOx trap catalysts usedto abate other pollutants in the stream. The sulfur tolerant NOx trapcatalyst composites are suitable for diesel engines because thecomposites can be regenerated at moderate temperatures with rich pulses,rather than at high temperatures.

[0190] The sulfur tolerant catalyst composite may optionally compriseconventional components known in the art.

[0191] In order to deposit the coat slurries on a macrosized carrier,one or more comminuted slurries are applied to the carrier in anydesired manner. Thus the carrier may be dipped one or more times in theslurry, with intermediate drying if desired, until the appropriateamount of slurry is on the carrier. The slurry employed in depositingthe catalytically-promoting metal component-high area support compositeon the carrier will often contain about 20% to 60% by weight offinely-divided solids, preferably about 25% to 55% by weight.

[0192] The sulfur tolerant catalyst composite of the present inventioncan be prepared and applied to a suitable substrate, preferably a metalor ceramic honeycomb carrier, or may be self-compressed. The comminutedcatalytically-promoting metal component-high surface area supportcomposite can be deposited on the carrier in a desired amount, forexample, the composite may comprise about 2% to 40% by weight of thecoated carrier, and is preferably about 5% to 30% by weight for atypical ceramic honeycomb structure. The composite deposited on thecarrier is generally formed as a coating over most, if not all, of thesurfaces of the carrier contacted. The combined structure may be driedand calcined, preferably at a temperature of at least about 250° C. butnot so high as to unduly destroy the high area of the refractory oxidesupport, unless such is desired in a given situation.

[0193] The carriers useful for the catalysts made by this invention maybe metallic in nature and be composed of one or more metals or metalalloys. The metallic carriers may be in various shapes such ascorrugated sheet or in monolithic form. Preferred metallic supportsinclude the heat-resistant, base-metal alloys, especially those in whichiron is a substantial or major component. Such alloys may contain one ormore of nickel, chromium, and aluminum, and the total of these metalsmay advantageously comprise at least about 15% by weight of the alloy,for instance, about 10% to 25% by weight of chromium, about 3% to 8% byweight of aluminum and up to about 20% by weight of nickel, say at leastabout 1% by weight of nickel, if any or more than a trace amount bepresent. The preferred alloys may contain small or trace amounts of oneor more other metals such as manganese, copper, vanadium, titanium andthe like. The surfaces of the metal carriers may be oxidized at quiteelevated temperatures, e.g. at least about 1000° C., to improve thecorrosion resistance of the alloy by forming an oxide layer on thesurface of carrier which is greater in thickness and of higher surfacearea than that resulting from ambient temperature oxidation. Theprovision of the oxidized or extended surface on the alloy carrier byhigh temperature oxidation may enhance the adherence of the refractoryoxide support and catalytically-promoting metal components to thecarrier.

[0194] Any suitable carrier may be employed, such as a monolithiccarrier of the type having a plurality of fine, parallel gas flowpassages extending there through from an inlet or an outlet face of thecarrier, so that the passages are open to fluid flow there through. Thepassages, which are essentially straight from their fluid inlet to theirfluid outlet, are defined by walls on which the catalytic material iscoated as a “washcoat” so that the gases flowing through the passagescontact the catalytic material. The flow passages of the monolithiccarrier are thin-walled channels which can be of any suitablecross-sectional shape and size such as trapezoidal, rectangular, square,sinusoidal, hexagonal, oval, circular. Such structures may contain fromabout 60 to about 600 or more gas inlet openings (“cells”) per squareinch of cross section. The ceramic carrier may be made of any suitablerefractory material, for example, cordierite, cordierite-alpha alumina,silicon nitride, zircon mullite, spodumene, alumina-silica magnesia,zircon silicate, sillimanite, magnesium silicates, zircon, petalite,alpha alumina and aluminosilicates. The metallic honeycomb may be madeof a refractory metal such as a stainless steel or other suitable ironbased corrosion resistant alloys.

[0195] The substrate can comprise a monolithic honeycomb comprising aplurality of parallel channels extending from the inlet to the outlet.The monolith can be selected from the group of ceramic monoliths andmetallic monoliths. The honeycomb can be selected from the groupcomprising flow through monoliths and wall flow monoliths. Suchmonolithic carriers may contain up to about 700 or more flow channels(“cells”) per square inch of cross section, although far fewer may beused. For example, the carrier may have from about 60 to 600, moreusually from about 200 to 400, cells per square inch (“cpsi”). Thesulfur tolerant catalyst composite can be coated in layers on amonolithic substrate generally which can comprise from about 0.50 g/in³to about 6.0 g/in³, preferably about 5.0 g/in³ to about 5.0 g/in³ ofcatalytic composition based on grams of composition per volume of themonolith.

[0196] The present invention includes a method comprising passing aninlet end fluid comprising an inlet end coating composition into asubstrate as recited above. For the purpose of the present invention afluid includes liquids, slurries, solutions, suspensions and the like.The aqueous liquid passes into the channel inlets and extending for atleast part of the length from the inlet end toward the outlet end toform an inlet end layer coating, with at least one inlet end coatingextending for only part of the length from the inlet end toward theoutlet end. A vacuum is applied to the outlet end while forcing a gasstream through the channels from the inlet end after the formation ofeach inlet end coating without significantly changing the length of eachinlet layer coating. At least one outlet end aqueous fluid comprising atleast one outlet end coating composition is passed into the substratethrough the at least some of the channel outlets at the substrate outletend. The aqueous liquid passes into the channels and extending for atleast part of the length from the outlet end toward the inlet end toform at least one outlet end layer coating. The method can furthercomprise applying a vacuum to the inlet end while forcing a gas streamthrough the channels from the outlet end after the formation of eachoutlet end coating without significantly changing the length of eachoutlet layer coating.

[0197] The method can further comprise the step of fixing the preciousmetal component selected from the inlet precious metal component of theinlet layer and the outlet precious metal component of the outlet layerto the respective inlet or outlet component selected from the inletrefractory oxide and inlet rare earth metal oxide components and theoutlet refractory oxide and outlet rare earth metal oxide components.The fixing can be conducted prior to coating the inlet and outletlayers. The step of fixing can comprise chemically fixing the preciousmetal component on the respective refractory oxide and/or rare earthmetal oxide. Alternatively, the step of fixing can comprise thermallytreating the precious metal component on the respective refractory oxideand/or rare earth metal oxide. The step of fixing comprises calciningthe precious metal component on the respective refractory oxide and/orrare earth metal oxide. The step of calcining can be conducted at from200° C., preferably 250° C. to 900° C. at from 0.1 to 10 hours. Thesteps of thermally fixing each layer are preferably conducted aftercoating and prior to coating a subsequent layer. The step of thermallytreating the substrate upon completion of coating all layers at from200° C. to 400° C. at from 1 to 10 seconds. The step of calcining ispreferably the substrate conducted upon completion of coating alllayers. The step of calcining is conducted at from 250° C. to 900° C. atfrom 0.1 to 10 hours.

[0198] Preferably, the precious metal can be prefixed on the supports.Alternatively the method further comprises fixing the soluble componentsin the layer such as one precious metal component to one of therefractory oxide or rare earth metal oxide components, the fixing beingconducted prior to coating the layers. The step of fixing can comprisechemically fixing the precious metal on the respective refractory oxideand/or rare earth metal oxide. More preferably, the step of fixingcomprises thermally treating the precious metal on the refractory oxideand/or rare earth metal oxide. The step of thermally treating thesubstrate upon completion of coating one or more layers at from 200° C.to 400° C. at from 1to 10, and preferably 2 to 6 seconds. The heat isprovided by forcing a gas stream, preferably air which is heated to from200° C. to 400° C. This temperature range has been found tosubstantially fix the soluble components such as precious metalcomponents. The combination of flow rate and temperature of the gasstream should be sufficient to heat the coating layer and preferably,providing a minimum of heat to the underlying substrate to enable rapidcooling in the subsequent cooling step prior to application ofsubsequent layers. Preferably, the steps of thermally fixing each layer,preferably followed by cooling with ambient air, are conducted aftercoating and prior to coating a subsequent layer. The cooling step ispreferably conducted using ambient air typically at from 5° C. to 40° C.at from 2 to 20, and preferably 4 to 10 seconds at a suitable flow rate.The combination of the ambient air flow rate and temperature of the gasstream should be sufficient to cool the coating layer. This methodpermits continuous coating of a plurality of layers on a substrate toform the above described article of the present invention. A preferredmethod comprises the step of fixing the precious metal component to therefractory oxide and rare earth metal oxide components, the fixing beingconducted prior to coating the first and second layers.

[0199] In yet another embodiment the method comprises the step ofapplying a vacuum to the partially immersed substrate at an intensityand a time sufficient to draw the coating media upwardly to apredesignated distance from the bath into each of the channels to form auniform coating profile therein for each immersion step. Optionally, andpreferably the substrate can be turned over to repeat the coatingprocess from the opposite end. The coated substrate should be thermallyfixed after forming the layer.

[0200] The method can include a final calcining step. This can beconducted in an oven between coating layers or after the coating of allthe layers on the substrate has been completed. The calcining can beconducted at from 250° C. to 900° C. at from 0.1 to 10 hours andpreferably from 450° C. to 750° C. at from at from 0.5 to 2 hours. Afterthe coating of all layers is complete the substrate can be calcined.

[0201] A method aspect of the present invention provides a method fortreating a gas containing noxious components comprising one or more ofcarbon monoxide, hydrocarbons and nitrogen oxides, by converting atleast some of each of the noxious components initially present toinnocuous substances such as water, carbon dioxide and nitrogen. Themethod comprises the step of contacting the gas under conversionconditions (e.g., a temperature of about 100° C. to 950° C. of the inletgas to the catalyst composition) with a catalyst composition asdescribed above.

[0202] In a specific embodiment, the present invention pertains to aphase with a hematite type composition and structure (assay 7). Thematerial is composed of a mixture of iron oxide, aluminum oxide, andsmall amounts of both yttrium oxide and strontium oxide. The iron oxidephase is not an exact match for hematite. The diffraction pattern is nota perfect match, slight shifts in peak position are noticed whencompared to a reference pattern of hematite. The work is directed attrying to manipulate the physical and or catalytic properties of simpleoxides by altering their structures. Small differences in composition orstructure can be the cause of changes in these properties or thedevelopment of new ones. An example would be the generation of apolarized structure in BaTiO₃ upon its distortion from a cubic to atetragonal structure, thus giving it valuable dielectric properties.This work centers on trying to determine if a small structural changecan be measured as a small change in lattice constants. To do this anaccurate determination of the unit cell constants is needed. It is alsoimportant to know the error associated with the measurement to know whentwo measured lattice parameters are really different.

[0203] Hematite is a primitive hexagonal cell. To determine the unitcell parameters, XRD data was collected on a NIST Sibley Ore sample(assay D20327) with White Rock 10 μm quartz as the internal standard.XRD data on an experimental sample (assay 7) was also collected usingthe same method. Both data sets were refined to obtain the unit cellparameters, a_(o) and c_(o). Results are tabulated below along with ICDDdata, reference card number 33-664. sample a_(o)(A) c_(o)(A) Assay 75.00821 (0.001166) 13.69433 (0.002883) experimental NIST hematite std5.03453 (0.002828) 13.75294 (0.00009) ICDD 5.036 13.749 No standardreference 33-664 deviations are given

[0204] The a_(o) and c_(o) values of the NIST hematite standard sampleclosely match those of the ICDD hematite reference card 33-664, althoughno standard deviations are given in the ICDD card. The close match ofthe experimental data with that of ICDD is a strong indication that thedata collection and refinement are acceptable. Thus, a valid comparisoncan be made between cell parameters of the sample assay 7 and those ofNIST hematite sample to determine whether the crystal structure of theassay 7 is truly different from a standard hematite.

[0205] The lattice parameters, for the phase with a hematite typestructure in assay 7 are a_(o)=5.00821(0.001166)Å andc_(o)=13.69433(0.002883)Å. Comparison of these lattice constants tothose of the hematite from NIST, which have been experimentallydetermined, indicates that they are different. The differences are wellbeyond the experimental error range. This difference may be due toimpurity atoms sitting on crystallographic sites or in interstitialsites. At present, the type or position of these impurity atoms cannotbe determined.

[0206] In a preferred embodiment, the present invention relates to amethod for removing NO_(x) contaminants from a SOx containing gaseousstream comprising the steps of:

[0207] (1) providing a catalyst composite;

[0208] (2) in a sorbing period, passing a lean gaseous stream comprisingNO_(x) and SO_(x) within a sorbing temperature range through thecatalyst composite to sorb at least some of the NO_(x) contaminants andthereby provide a NO_(x) depleted gaseous stream exiting the catalystcomposite and to sorb and abate at least some of the SO_(x) contaminantsin the gaseous stream and thereby provide a SO_(x) depleted gaseousstream exiting the catalyst composite;

[0209] (3) in a NO_(x) desorbing and abating period, changing the leangaseous stream to a rich gaseous stream to thereby reduce and desorb atleast some of the NO_(x) contaminants from the catalyst composite andthereby provide a reduced NO_(x) enriched gaseous stream exiting thecatalyst composite;

[0210] (4) in a SOx desorbing period, changing the lean gaseous streamto a rich gaseous stream and raising the temperature of the gaseousstream to within a desorbing temperature range to thereby reduce anddesorb at least some of the SO_(x) contaminants from the catalystcomposite and thereby regenerate the catalyst composite and provide areduced SO_(x) enriched gaseous stream exiting the catalyst composite;and wherein the catalyst composite comprises:

[0211] (a) a platinum component;

[0212] (b) a support; and

[0213] (c) a NOx sorbent component comprising the followingconstituents:

[0214] (i) Na₂O in an amount up to about 0.1%;

[0215] (ii) MgO in an amount up to about 1%;

[0216] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0217] (iv) SrO in an amount from about 0.5% to about 15%;

[0218] (v) Y₂O₃ in an amount up to about 5%; and

[0219] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0220] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0221] (i) providing an aqueous suspension or solution of theconstituents of the NOx sorbent component;

[0222] (ii) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0223] (iii) separating the precipitate from the mother liquor.

[0224] In another preferred embodiment, the present invention relates toa catalyst composite prepared by a hydrothermal synthesis method whichcomprises the steps of:

[0225] (a) providing an aqueous suspension or solution of a NOx sorbentcomponent comprising the following constituents:

[0226] (i) Na₂O in an amount up to about 0.1%;

[0227] (ii) MgO in an amount up to about 1%;

[0228] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0229] (iv) SrO in an amount from about 0.5% to about 15%;

[0230] (v) Y₂O₃ in an amount up to about 5%; and

[0231] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0232] (b) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0233] (c) separating the precipitate from the mother liquor; and

[0234] (d) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0235] In yet another preferred embodiment, the present inventionrelates to a method of forming a catalyst composite which comprises thesteps of:

[0236] (a) providing an aqueous suspension or solution of a NOx sorbentcomponent comprising the following constituents:

[0237] (i) Na₂O in an amount up to about 0.1%;

[0238] (ii) MgO in an amount up to about 1%;

[0239] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0240] (iv) SrO in an amount from about 0.5% to about 15%;

[0241] (v) Y₂O₃ in an amount up to about 5%; and

[0242] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0243] (b) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0244] (c) separating the precipitate from the mother liquor; and

[0245] (d) forming an admixture of the precipitate, a platinumcomponent, and a support.

[0246] In still another preferred embodiment, the present inventionrelates to a method of forming a catalyst composite which comprises thesteps of:

[0247] (1) forming an admixture of:

[0248] (a) a support; and

[0249] (b) a NOx sorbent component comprising the followingconstituents:

[0250] (i) Na₂O in an amount up to about 0.1%;

[0251] (ii) MgO in an amount up to about 1%;

[0252] (iii) Fe₂O₃ in an amount from about 10% to about 30%;

[0253] (iv) SrO in an amount from about 0.5% to about 15%;

[0254] (v) Y₂O₃ in an amount up to about 5%; and

[0255] (vi) the remainder of the NOx sorbent component being Al₂O₃;

[0256] (2) combining a water-soluble or dispersible platinum componentand the admixture from step (1) with an aqueous liquid to form asolution or dispersion which is sufficiently dry to absorb essentiallyall of the liquid;

[0257] (3) forming a layer of the solution or dispersion on a substrate;and

[0258] (4) converting the platinum component in the resulting layer to awater-insoluble form;

[0259] wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of:

[0260] (i) providing an aqueous suspension or solution of theconstituents of the NOx sorbent component;

[0261] (ii) subjecting the suspension or solution of the constituents ofthe NOx sorbent component to a temperature from about 150° C. to about300° C. in an autoclave under pressure for a time sufficient to producea precipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and

[0262] (iii) separating the precipitate from the mother liquor.

[0263] In this preferred embodiment, the NOx sorbent component mayfurther comprise BaO in an amount from about 0.5% to about 15%.

[0264] The following examples are provided to further illustrate variousembodiments of this invention and to provide a comparison between theenumerated catalysts of this invention and prior art catalysts. Theexamples are provided to illustrate the nature of the claimed processand are not intended to limit the scope of the claimed invention. Unlessotherwise stated, parts and percentages in the examples are given byweight.

EXAMPLES Preparation of Sulfur Tolerant NOx Trap Materials Example 1(E1)

[0265] Weighed the following precursors: Aluminum acetate Al—Ac(Boehmite, AlOOH, containing 65.4 wt % Al₂O₃) 1422.02 g; Barium acetateBa—Ac (containing BaO 60 wt %) 625 g; cerium nitrate Ce—N aqueoussolution (containing CeO₂30.6 wt %) 637.2 g.

[0266] Barium acetate was first dissolved in deionized water. Ceriumnitrate was also dissolved in deionized water. The solution had a pH of7.62. Al—Ac was added into the Ba—Ac solution under constant stirring.Deionized water was added and the final slurry had a pH of 6.32. Ceriumnitrate solution was added into the slurry. Continued to mix for 1 hour,and pH dropped to 5.75. The slurry started to gel. Mixing was continuedovernight and the gel thickened like jelly. Additional deionized waterwas added to the gel to thin it and to bring the total volume to 12liters. The gel was transferred to a 5-gallon autoclave for hydrothermalsynthesis.

[0267] The autoclave was heated to 232° C., kept at 232° C. for 2 hours,then cooled down to room temperature. Soaked at room temperature for 60hours, the autoclave was heated up to 230° C. The hydrothermal processat 230° C. was continued for 48 hours, then cooled down to roomtemperature.

[0268] The product was centrifuged. The mother liquor had a pH of 4.68.The precipitate was washed with deionized water and centrifuged again.The product was dried overnight and calcined at 550° C. for 2 hours in abox furnace. The final product had a BET surface area of 62 m²/g. XRFsemi quantitative analysis indicated the final composite to be 84.7 wt %Al₂O₃-11.5 wt % CeO₂-2.4 wt % BaO.

Example 2 (E2)

[0269] Trap material E2 was made by hydrothermal synthesis and preparedas follows. Weighed the following precursors: 45.04 g of aluminumacetate Al—Ac (Boehmite, AlOOH, containing 65.4 wt % Al₂O₃); 44.59 g ofcobalt nitrate Co—N (containing 22.5 wt % of CoO); and 34.135 g oflanthanum nitrate La—N solution (containing 27.1 wt % La₂O₃).

[0270] Co—N was dissolved in La—N solution, deionized water was added tocompletely dissolve the Co salt. The final solution had a pH of 1.23.Al—Ac was added into 250 g of deionized water under constant stirring.The slurry had a pH of 5.29. The nitrate solution was added into theslurry under vigorous stirring. Gradually the mixed slurry started togel. At this stage, the measured pH was 4.96. Ammonia of 10%concentration was added dropwise, until pH increased to 7.60 and thecolor of the gel turned to blue-green. Transferred the gel intoautoclave. The hydrothermal synthesis was processed for 64 hours at 250°C. The product was washed and centrifuged, then dried and calcined at550° C. for 2 hours. XRF semi quantitative resulted in 79 wt % Al₂O₃-19wt % Co₃O₄-1 wt % La₂O₃.

Example 3 (E3)

[0271] The sample was made by hydrothermal synthesis. The composition ofthe sample was (XRF) 25.2 wt % BaO-11.0 wt % CeO₂-63.8 wt % Al₂O₃.

Example 4 (E4)

[0272] The sample was made by hydrothermal synthesis. The nominalcomposition of the sample was 25 wt % SrO-32 wt % TiO₂-43 wt % Al₂O₃.

Example 5 (E5)

[0273] This is a sample whose composition is the same as sample Example3 but not made by hydrothermal synthesis. Example 5 was made byco-precipitation. Precursors cerium nitrate (39.63 wt % CeO₂), bariumacetate (60.6 wt % BaO), aluminum acetate (65.5 wt % Al₂O₃), were used.Al—Ac was added into the Ba—Ac aqueous solution under vigorous stirringto make a slurry. Acetic acid was added dropwise into the slurry. pHdecreased to between 6 and 5, and the slurry started to gel. Ce—Nsolution was added into the gel under stirring. Acetic acid was addedand pH approached 5. The gel was transferred into a crucible and driedat 150° C. overnight. The dried material was ground and sieved to 250um. The granules were calcined at 300 C. for 4 hours then 450° C. for 6hours.

Preparation of the Trap Testing Samples for Mini-reactor Examples of NOxTrap Testing Samples (Samples T1 to T5)

[0274] Sample preparation: The above materials (E1 to E5) wereimpregnated with anionic Pt solution to obtain 1 wt % of Pt loadingdispersed on the trap material. The impregnated sample was dried andcalcined at 450° C. for 1 hour to form dry chunks. The chunks werecrushed and sieved to obtain particles of diameter of average 300 umgrains. Thus, corresponding to the trap materials E1 to E5, trappingtest samples were obtained and designated as T1 to T5 what were 300 umgranular particles loaded with 1 wt % Pt.

Test Methods of NOx Trapping and Sulfur Regeneration Testing Protocoland CO Injection Mode

[0275] Lean gas flow was used to load the trap with NOx and SOx; richflow was used to release NOx (and SOx) and regenerate sulfur from thesample. Synchronized valves were used to simultaneously close/open O2/COgas lines to inject CO (or vise versa to inject O2). O₂ NO CO N₂ SO₂Rich  0 500 ppm 2.2% balance 60 ppm Lean 10% 500 ppm 0 balance 60 ppm

[0276] The Lean/Rich cycle was set alternatively at 5 minutes lean and 5seconds rich with VHSV 50,000/hr. or 25,000/hr.

[0277] Note that a high level of SOx (60 ppm) was used in this test.Modem commercial diesel fuel containing 350 ppm sulfur would generate 20ppm SO2 in the exhaust gas stream. Hence, the 60 ppm SOx level used inthis test is 3 times that expected in modern commercial diesel fuel.

[0278] NOx and SOx base lines were determined first with an empty tubeprior to the test. Sample of the trap material was loaded in the reactortube with a 50:50 mixture with cordierite particles. In an alternativelean/rich mode, NO level, as a function of sulfur poisoning andregeneration, was observed and recorded.

[0279] After the experiment started, the NO level in the exit of thecatalyst increases gradually with time, because more and more sulfur wasadsorbed on the NOx trap. The degradation of NO conversion is anindication of “the degree of NOx trap being poisoned in SO2environment.” A degraded NOx trap was then regenerated at a giventemperature. Observation and recording of NOx trap performance was thenrepeated. A good regenerated NOx trap should show a NO conversion levelas if it had not been poisoned.

[0280] Unless specified, the NOx performance test was carried out at aconstant temperature, 300° C.

[0281] Test Procedure

[0282] Sample is aged at 700° C. for 2 hours in air (oven) before test.

[0283] NOx and SOx base lines were determined without catalyst first inthe reactor prior to run the sample.

[0284] Test tube loading: sample T2 was loaded in the reactor tube aswell mixed (100 mg trap material)+(100 mg cordierite, diluent); othersamples (50 mg trap material)+(50 mg cordierite); total gas flow was 100sccm. There was a VHSV: 25,000/hr and an equivalent of 200 g/(ft)3 Ptloading for T2; VHSV: 50,000/hr and an equivalent of 100 g/(ft)3 Ptloading for other samples (T1, T3, T4 and T5).

[0285] At 300° C. constant temperatures, ran lean/rich cycles for 2hours and recorded the level of NO changes. When the catalyst waspoisoned by S, the NOx level should increase gradually. Then the NOx/SOxtrap was regenerated at a given temperature (e.g. 450° C., 500° C., 550°C.) for 15 minutes. After regeneration of S, NOx trap function wasretested. Compare the NOx level with original level to verify theeffectiveness of regeneration.

Result 1 Comparison of Performance of NOx Trap Samples in Lean/Rich ModeBeing Sulfated and Regenerated

[0286] The % NO conversion is tabulated in the following table. Higher %NO conversion indicates a more effective NOx trap performance, lower %NO a less effective NOx trap, either poisoned by sulfur and/or lessregenerated by the regeneration process.

% NO conversion−poisoned by SO2 and the recovery after regeneration

[0287] sample A A′ B C D regeneration T1 (E1) 68% — 46% — 68% 400° C. T2(E2)* 75% — 74% 73% 77% 400° C. T3 (E3) 58% — 46% — 70% 550° C. T4 (E4)77% — 68% — 77% 500° C. T5 (E5) 31% 19% — — — **cannot be regenerated @550 C.

[0288] A:initial NO conversion of a fresh sample w/o sulfur

[0289] A′:exposed to 60 ppm SO₂ for 15 minutes

[0290] B:exposed to 60 ppm SO₂ for 1 hour.

[0291] C:exposed to 60 ppm SO₂ for 2 hours.

[0292] D:after regeneration for 15 minutes.

Results 2 Performance of Continuous Trapping NOx in Prolong Length ofTime in Sulfur Environment Without Regeneration

[0293] Sample T2 has exposed to 60 ppm SO₂ for prolong length of time.After 22 hours, the NO conversion level kept at 49%. At 300° C. workingtemperature, sulfur could be partially regenerated and therefore the NOxtrap T2 remained active (at a lower level). In this sense, T2 was asulfur resistant NOx trap.

Example 6 (E6)

[0294] This example illustrates a NOx trap sample prepared with Fe asone of the key components. The results of a model gas reactor clearlyshowed that the sample was capable of partially regenerate sulfur at the300° C. operation temperature, while it also performed NOx trap functionat the same time. The NOx trap was a sulfur resistant NOx trap and itwould maintain certain amount of NOx activity for practically no limitof time.

[0295] Forty five point zero four grams of aluminum acetate Al—Ac (65.5wt % Al₂O₃), 55.80 grams of iron nitrate Fe—N (14.0 wt %, Fe), and 34.14grams of lanthanum nitrate La—N solution (27.1 wt % La₂O₃) precursorswere weighed. Iron nitrate was dissolved in lanthanum nitrate solution.A slurry of Al—Ac was made with 200 grams of D. I. Water. The slurry wasconstantly stirred for 2 hours and started to gel. The nitrate solutionwas added into Al—Ac slurry. A thick dark brown gel was formed. The gelwas aged over night. A pH 3.5 was measured. The aged gel was submittedfor hydrothermal treatment at 250° C. for 72 hours. The precipitate wasseparated from mother liquor, washed once, and dried over night. Themother liquor had a pH<3.

Preparation of the Test Sample for Mini-reactor Example T6

[0296] The same test sample preparation method was used in preparing T6.T6 was made from E6, having granular shape of 300 um diameter and loadedwith 1 wt % Pt.

Testing Results

[0297] Test method was the same as used in T1 to T5, with a 50 mg sampleloading and 50,000/hr. VHSV. In 60 ppm SO₂ environment, the time zero NOconversion was 57%, then reduced to 47% after 1 hour, and 50% 2 hours.However, the zero time activity increased to 70% after a 500 C.regeneration. After a long period of continuous test, the trap stillshowed NOx activity. After 68 hours, the NO conversion was 47%.Considering that the amount of SO₂ flew through was (calculated) about 1mg per hour, there were 68 mg of SO₂ passing the 50 mg sample in 68hours. This clearly showed that the sample was capable of partiallyregenerate sulfur at 300° C. operation temperature, while it alsoperformed NOx trap function at the same time. NOx trap T6 was a sulfurresistant NOx trap and it would maintain certain amount of NOx activityfor practically no limit of time. The sulfur regeneration temperaturewas quite low. After the 68 hours continuous test, the NOx activity wasrecovered with 400° C. sulfur regeneration.

Example 7

[0298] Assay 7 was hand ground in a mortar and pestle. White Rock 10μquartz was added as an internal standard and the two powders werehomogenized. The mixture was then backpacked into a cavity in a flatplate mount. X-ray diffraction data was collected with a Philipsvertical goniometer with generator settings of 45 kV and 40 mA. The scanrange was from 20° to 900°2θ using a step size of 0.02°2θ and a 10second count time per step. The assay contains bohmite, a transitionalumina, and a phase close in structure to hematite. Quartz, theinternal standard is also present, see the spectra below. The peakscorresponding to those of the quartz internal standard were profile fitfirst to determine the peak centroid and intensity. A calibration curvewas generated by a polynomial fit to this data. The raw data was thencalibrated using this curve. Next the peaks corresponding to those ofthe “hematite” phase were profile fit to determine their peak centroidsand intensities. A unit cell was refined using the profile fit peaklocations, the hkl indices of each peak, and the space group forhematite which is R-3c. Initial lattice parameters were taken fromreference card 33-664. To check this work data was collected on a NISTiron ore standard composed primarily of hematite. Traces of quartz andmaghemite were also present. The assay number for this sample isD20328N. The scan range was from 19° to 86°2θ using a step size of0.02°2θ and a 10 second count time per step. White Rock 10μ quartz wasused as the internal standard. The raw data was processed in the samefashion as assay

[0299] While the invention has been described in detail with respect tospecific embodiments thereof, such embodiments are illustrative and thescope of the invention is defined in the appended claims.

We claim:
 1. A method for removing NO_(x) contaminants from a SOxcontaining gaseous stream comprising the steps of: (1) providing acatalyst composite; (2) in a sorbing period, passing a lean gaseousstream comprising NO_(x) and SO_(x) within a sorbing temperature rangethrough the catalyst composite to sorb at least some of the NO_(x)contaminants and thereby provide a NO_(x) depleted gaseous streamexiting the catalyst composite and to sorb and abate at least some ofthe SO_(x) contaminants in the gaseous stream and thereby provide aSO_(x) depleted gaseous stream exiting the catalyst composite; (3) in aNO_(x) desorbing and abating period, changing the lean gaseous stream toa rich gaseous stream to thereby reduce and desorb at least some of theNO_(x) contaminants from the catalyst composite and thereby provide areduced NO_(x) enriched gaseous stream exiting the catalyst composite;(4) in a SOx desorbing period, changing the lean gaseous stream to arich gaseous stream and raising the temperature of the gaseous stream towithin a desorbing temperature range to thereby reduce and desorb atleast some of the SO_(x) contaminants from the catalyst composite andthereby regenerate the catalyst composite and provide a reduced SO_(x)enriched gaseous stream exiting the catalyst composite; and wherein thecatalyst composite comprises: (a) a platinum component; (b) a support;and (c) a NOx sorbent component comprising a first metal oxide and asecond metal oxide, wherein the metal in the first metal oxide isselected from the group consisting of aluminum, titanium, zirconium,silicon, and composites thereof, and the metal in the second metal oxideis selected from the group consisting of Group IIA metals, Group IIImetals, Group IV metals, rare earth metals, and transition metals;wherein the metal in the first metal oxide is different from the metalin the second metal oxide; wherein the NOx sorbent component is preparedby a hydrothermal synthesis process comprising the steps of: (i)providing an aqueous suspension or solution of the first and secondmetal oxides, or precursors thereof, or both, wherein the precursors ofthe first and second metal oxides are metal salts which when hydrolyzedproduce the respective metal oxides; (ii) subjecting the suspension orsolution of the first and second metal oxides, or precursors thereof, toa temperature from about 150° C. to about 300° C. in an autoclave underpressure for a time sufficient to produce a precipitate having anaverage particle size from about 0.001 to about 0.2 micron in a motherliquor; and (iii) separating the precipitate from the mother liquor. 2.The method according to claim 1, wherein the SOx desorbing temperaturerange in (4) is greater than about 300° C.
 3. The method according toclaim 2, wherein the SOx desorbing temperature range in (4) is greaterthan about 350° C.
 4. The method according to claim 3, wherein the SOxdesorbing temperature range in (4) is greater than about 400° C.
 5. Themethod according to claim 4, wherein the SOx desorbing temperature rangein (4) is greater than about 450° C.
 6. The method according to claim 1,further comprising a platinum group metal component other than platinum.7. The method according to claim 6, wherein the platinum group metalcomponent is selected from the group consisting of palladium, rhodium,ruthenium, and iridium components, and mixtures thereof.
 8. The methodaccording to claim 1, wherein the support is selected from the groupconsisting of alumina, silica, titania, and zirconia compounds.
 9. Themethod according to claim 1, wherein the support is selected from thegroup consisting of activated alumina, alumina-ceria, alumina-chromia,alumina-silica, alumina-zirconia, silica, silica-titania,silica-titania-alumina, silica-titania-zirconia, titania, zirconia,zirconia-titania, and zirconia-alumina-titania.
 10. The method accordingto claim 1, wherein the metal in the second metal oxide is selected fromthe group consisting of magnesium, calcium, strontium, barium, scandium,titanium, zirconium, hafnium, lanthanum, cerium, praseodymium,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, ytterbium, vanadium, chromium, manganese, iron, cobalt,nickel, copper, and zinc.
 11. The method according to claim 10, whereinthe metal in the second metal oxide is selected from the groupconsisting of barium, lanthanum, cerium, iron, cobalt, and copper. 12.The method according to claim 1, wherein the metals in the first andsecond metal oxides are selected from the group consisting ofaluminum/cerium/barium, aluminum/copper/lanthanum,aluminum/cobalt/lanthanum, and iron/aluminum.
 13. The method accordingto claim 1, wherein the metal in the first metal oxide and the metal inthe second metal oxide are present in a mole ratio from about 3:7 toabout 9:1, respectively.
 14. The method according to claim 13, whereinthe metal in the first metal oxide an d the metal in the second metaloxide are present in a mole ratio from about 4:6 to about 8.5:1.5,respectively.
 15. The method according to claim 1, wherein the catalystcomposite comprises: (i) at least about 1 g/ft³ o f the platinumcomponent; (ii) from about 0.15 g/in³ to about 6.0 g/in³ of the support;and (iii) from about 0.025 g/in³ to about 4 g/in³ of the NO_(x) sorbentcomponent.
 16. The method according to claim 1, wherein the precursorsof the first metal oxide and second metal oxide arewater-soluble/dispersible metal salts selected from the group consistingof acetates, nitrates, hydroxides, oxychlorides, hydroxychlorides,carbonates, sulfates, oxalates, and tartrates.
 17. The method accordingto claim 1, wherein the suspension or solution of metal hydroxides in(4)(c)(ii) is subjected to a temperature from about 175° C. to about250° C.
 18. The method according to claim 1, wherein the precipitate in(4)(c)(ii) has an average particle size from about 0.01 to about 0.2micron.
 19. The method according to claim 1, wherein the catalystcomposite is supported on a metal or ceramic honeycomb carrier or isself-compressed.
 20. The method according to claim 1, wherein the NOxsorbent component further comprises a third metal oxide, wherein themetal in the third metal oxide is selected from the group consisting ofaluminum, titanium, zirconium, silicon, and composites thereof, and themetal in the second metal oxide is selected from the group consisting ofGroup IIA metals, Group III metals, Group IV metals, rare earth metals,and transition metals; wherein the metal in the third metal oxide isdifferent from the metals in the first and second metal oxides.
 21. Acatalyst composite prepared by a hydrothermal synthesis method whichcomprises the steps of: (i) providing an aqueous suspension or solutionof a first metal oxide and a second metal oxide, or precursors thereof,or both, wherein the precursors of the first and second metal oxides aremetal salts which when hydrolyzed produce the respective metal oxides;(ii) subjecting the suspension or solution of the first and second metaloxides, or precursors thereof, to a temperature from about 150° C. toabout 300° C. in an autoclave under pressure for a time sufficient toproduce a precipitate having an average particle size from about 0.001to about 0.2 micron in a mother liquor; and (iii) separating theprecipitate from the mother liquor; and (iv) forming an admixture of theprecipitate, a platinum component, and a support.
 22. The catalystcomposite according to claim 21, further comprising, in step (iv), thestep of admixing a platinum group metal component other than platinum.23. The catalyst composite according to claim 21, wherein the platinumgroup metal component is selected from the group consisting ofpalladium, rhodium, ruthenium, and iridium components, and mixturesthereof.
 24. The catalyst composite according to claim 21, wherein thesupport, in step (iv), is selected from the group consisting of alumina,silica, titania, and zirconia compounds.
 25. The catalyst compositeaccording to claim 21, wherein the support, in step (iv), is selectedfrom the group consisting of activated alumina, alumina-ceria,alumina-chromia, alumina-silica, alumina-zirconia, silica,silica-titania, silica-titania-alumina, silica-titania-zirconia,titania, zirconia, zirconia-titania, and zirconia-alumina-titania. 26.The catalyst composite according to claim 21, wherein the metal in thesecond metal oxide is selected from the group consisting of magnesium,calcium, strontium, barium, scandium, titanium, zirconium, hafnium,lanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc.27. The catalyst composite according to claim 26, wherein the metal inthe second metal oxide is selected from the group consisting of barium,lanthanum, cerium, iron, cobalt, and copper.
 28. The catalyst compositeaccording to claim 21, wherein the metals in the first and second metaloxides are selected from the group consisting of aluminum/cerium/barium,aluminum/copper/lanthanum, aluminum/cobalt/lanthanum, and iron/aluminum.29. The catalyst composite according to claim 21, wherein the metal inthe first metal oxide and the metal in the second metal oxide arepresent in a ratio from about 3:7 to about 9:1, respectively.
 30. Thecatalyst composite according to claim 29, wherein the metal in the firstmetal oxide and the metal in the second metal oxide are present in aratio from about 4:6 to about 8.5:1.5, respectively.
 31. The catalystcomposite according to claim 21, wherein the catalyst compositecomprises: (i) at least about 1 g/ft³ of the platinum component; (ii)from about 0.15 g/in³ to about 6.0 g/in³ of the support; and (iii) fromabout 0.025 g/in³ to about 4 g/in³ of the NO_(x) sorbent component. 32.The catalyst composite according to claim 21, wherein the precursors ofthe first metal oxide and second metal oxide arewater-soluble/dispersible metal salts selected from the group consistingof acetates, nitrates, hydroxides, oxychlorides, hydroxychlorides,carbonates, sulfates, oxalates, and tartrates.
 33. The catalystcomposite according to claim 21, wherein the suspension or solution ofmetal hydroxides in (ii) is subjected to a temperature from about 175°C. to about 250° C.
 34. The catalyst composite according to claim 21,wherein the precipitate in step (ii) has an average particle size fromabout 0.01 to about 0.2 micron.
 35. The catalyst composite according toclaim 21, wherein the catalyst composite is supported on a metal orceramic honeycomb carrier or is self-compressed
 36. The catalystcomposite according to claim 21, wherein the NOx sorbent componentfurther comprises a third metal oxide, wherein the metal in the thirdmetal oxide is selected from the group consisting of aluminum, titanium,zirconium, silicon, and composites thereof, and the metal in the secondmetal oxide is selected from the group consisting of Group IIA metals,Group III metals, Group IV metals, rare earth metals, and transitionmetals; wherein the metal in the third metal oxide is different from themetals in the first and second metal oxides.
 37. A method of forming acatalyst composite which comprises the steps of: (i) providing anaqueous suspension or solution of a first metal oxide and a second metaloxide, or precursors thereof, or both, wherein the precursors of thefirst and second metal oxides are metal salts which when hydrolyzedproduce the respective metal oxides; (ii) subjecting the suspension orsolution of the first and second metal oxides, or precursors thereof, toa temperature from about 150° C. to about 300° C. in an autoclave underpressure for a time sufficient to produce a precipitate having anaverage particle size from about 0.001 to about 0.2 micron in a motherliquor; and (iii) separating the precipitate from the mother liquor; and(iv) forming an admixture of the precipitate, a platinum component, anda support.
 38. A method of forming a catalyst composite which comprisesthe steps of: (1) forming an admixture of: (a) a support; and (b) a NOxsorbent component; (2) combining a water-soluble or dispersible platinumcomponent and the admixture from step (1) with an aqueous liquid to forma solution or dispersion which is sufficiently dry to absorb essentiallyall of the liquid; (3) forming a layer of the solution or dispersion ona substrate; and (4) converting the platinum component in the resultinglayer to a water-insoluble form; wherein the NOx sorbent component isprepared by a hydrothermal synthesis process comprising the steps of:(i) providing an aqueous suspension or solution of a first metal oxideand a second metal oxide, or precursors thereof, or both, wherein theprecursors of the first and second metal oxides are metal salts whichwhen hydrolyzed produce the respective metal oxides; (ii) subjecting thesuspension or solution of the first and second metal oxides, orprecursors thereof, to a temperature from about 150° C. to about 300° C.in an autoclave under pressure for a time sufficient to produce aprecipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and (iii) separating the precipitate fromthe mother liquor.
 39. A method for removing NO_(x) contaminants from aSOx containing gaseous stream comprising the steps of: (1) providing acatalyst composite; (2) in a sorbing period, passing a lean gaseousstream comprising NO_(x) and SO_(x) within a sorbing temperature rangethrough the catalyst composite to sorb at least some of the NO_(x)contaminants and thereby provide a NO_(x) depleted gaseous streamexiting the catalyst composite and to sorb and abate at least some ofthe SO_(x) contaminants in the gaseous stream and thereby provide aSO_(x) depleted gaseous stream exiting the catalyst composite; (3) in aNO_(x) desorbing and abating period, changing the lean gaseous stream toa rich gaseous stream to thereby reduce and desorb at least some of theNO_(x) contaminants from the catalyst composite and thereby provide areduced NO_(x) enriched gaseous stream exiting the catalyst composite;(4) in a SOx desorbing period, changing the lean gaseous stream to arich gaseous stream and raising the temperature of the gaseous stream towithin a desorbing temperature range to thereby reduce and desorb atleast some of the SO_(x) contaminants from the catalyst composite andthereby regenerate the catalyst composite and provide a reduced SO_(x)enriched gaseous stream exiting the catalyst composite; and wherein thecatalyst composite comprises: (a) a platinum component; (b) a support;and (c) a NOx sorbent component comprising the following constituents:(i) Na₂O in an amount up to about 0.1%; (ii) MgO in an amount up toabout 1%; (iii) Fe₂O₃ in an amount from about 10% to about 30%; (iv) SrOin an amount from about 0.5% to about 15%; (v) Y₂O₃ in an amount up toabout 5%; and (vi) the remainder of the NOx sorbent component beingAl₂O₃; wherein the NOx sorbent component is prepared by a hydrothermalsynthesis process comprising the steps of: (i) providing an aqueoussuspension or solution of the constituents of the NOx sorbent component;(ii) subjecting the suspension or solution of the constituents of theNOx sorbent component to a temperature from about 150° C. to about 300°C. in an autoclave under pressure for a time sufficient to produce aprecipitate having an average particle size from about 0.001 to about0.2 micron in a mother liquor; and (iii) separating the precipitate fromthe mother liquor.
 40. The method according to claim 39, wherein the NOxsorbent component further comprises BaO in an amount from about 0.5% toabout 15%.
 41. A catalyst composite prepared by a hydrothermal synthesismethod which comprises the steps of: (a) providing an aqueous suspensionor solution of a NOx sorbent component comprising the followingconstituents: (i) Na₂O in an amount up to about 0.1%; (ii) MgO in anamount up to about 1%; (iii) Fe₂O₃ in an amount from about 10% to about30%; (iv) SrO in an amount from about 0.5% to about 15%; (v) Y₂O₃ in anamount up to about 5%; and (vi) the remainder of the NOx sorbentcomponent being Al₂O₃; (b) subjecting the suspension or solution of theconstituents of the NOx sorbent component to a temperature from about150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and (c) separatingthe precipitate from the mother liquor; and (d) forming an admixture ofthe precipitate, a platinum component, and a support.
 42. The catalystcomposite according to claim 41, wherein the NOx sorbent componentfurther comprises BaO in an amount from about 0.5% to about 15%.
 43. Amethod of forming a catalyst composite which comprises the steps of: (a)providing an aqueous suspension or solution of a NOx sorbent componentcomprising the following constituents: (i) Na₂O in an amount up to about0.1%; (ii) MgO in an amount up to about 1%; (iii) Fe₂O₃ in an amountfrom about 10% to about 30%; (iv) SrO in an amount from about 0.5% toabout 15%; (v) Y₂O₃ in an amount up to about 5%; and (vi) the remainderof the NOx sorbent component being Al₂O₃; (b) subjecting the suspensionor solution of the constituents of the NOx sorbent component to atemperature from about 150° C. to about 300° C. in an autoclave underpressure for a time sufficient to produce a precipitate having anaverage particle size from about 0.001 to about 0.2 micron in a motherliquor; and (c) separating the precipitate from the mother liquor; and(d) forming an admixture of the precipitate, a platinum component, and asupport.
 44. The method according to claim 43, wherein the NOx sorbentcomponent further comprises BaO in an amount from about 0.5% to about15%.
 45. A method of forming a catalyst composite which comprises thesteps of: (1) forming an admixture of: (a) a support; and (b) a NOxsorbent component comprising the following constituents: (i) Na₂O in anamount up to about 0.1%; (ii) MgO in an amount up to about 1%; (iii)Fe₂O₃ in an amount from about 10% to about 30%; (iv) SrO in an amountfrom about 0.5% to about 15%; (v) Y₂O₃ in an amount up to about 5%; and(vi) the remainder of the NOx sorbent component being Al₂O₃; (2)combining a water-soluble or dispersible platinum component and theadmixture from step (1) with an aqueous liquid to form a solution ordispersion which is sufficiently dry to absorb essentially all of theliquid; (3) forming a layer of the solution or dispersion on asubstrate; and (4) converting the platinum component in the resultinglayer to a water-insoluble form; wherein the NOx sorbent component isprepared by a hydrothermal synthesis process comprising the steps of:(i) providing an aqueous suspension or solution of the constituents ofthe NOx sorbent component; (ii) subjecting the suspension or solution ofthe constituents of the NOx sorbent component to a temperature fromabout 150° C. to about 300° C. in an autoclave under pressure for a timesufficient to produce a precipitate having an average particle size fromabout 0.001 to about 0.2 micron in a mother liquor; and (iii) separatingthe precipitate from the mother liquor.
 46. The method according toclaim 45, wherein the NOx sorbent component further comprises BaO in anamount from about 0.5% to about 15%.